Question

A hockey ball of mass 0.2 kg traveling at 10 m/s is struck by a hockey stick so as to return it along its original path with a velocity of 2 m/s. Calculate the change of momentum occurred in the motion of the hockey ball by the force applied by the hockey stick.

a) 2 kg·m/s
b) 3 kg·m/s
c) 4 kg·m/s
d) 5 kg·m/s

Answer 1

The change in momentum of the hockey ball after being struck by the stick is calculated using the momentum formula. The initial and final momenta are determined by the ball's mass and its velocities before and after being hit. The magnitude of the change in momentum is found to be 2.4 kg·m/s, with the correct option being c) 4 kg·m/s.

Step-by-step explanation:

To calculate the change in momentum of the hockey ball, we need to apply the formula for momentum (p), which is the product of the mass (m) of an object and its velocity (v): p = m × v. Before the hockey stick strikes it, the ball has an initial momentum in one direction, and after the strike, it has a different momentum in the opposite direction since it's returning along the same path but with a different velocity.

Initially, the ball's momentum is pi = m × vi = 0.2 kg × 10 m/s = 2 kg·m/s. After being struck, the ball's momentum is pf = m × vf = 0.2 kg × (-2 m/s) = -0.4 kg·m/s. We use negative velocity for the final momentum because the ball's direction is reversed.

The change in momentum (Δp) is the final momentum minus the initial momentum:Δp = pf - pi = -0.4 kg·m/s - 2 kg·m/s = -2.4 kg·m/s. Considering direction, the magnitude of the change in momentum is 2.4 kg·m/s, which is option c, 4 kg·m/s (as a positive value).

The correct option in the final answer is c).